U.S. patent application number 10/806401 was filed with the patent office on 2004-09-30 for setting method for control parameter, setting device for control parameter, and electric power steering device.
This patent application is currently assigned to TOYODA KOKI KABUSHIKI KAISHA. Invention is credited to Asada, Atsuhisa.
Application Number | 20040188170 10/806401 |
Document ID | / |
Family ID | 32821522 |
Filed Date | 2004-09-30 |
United States Patent
Application |
20040188170 |
Kind Code |
A1 |
Asada, Atsuhisa |
September 30, 2004 |
Setting method for control parameter, setting device for control
parameter, and electric power steering device
Abstract
A method for setting a control parameter for an electric power
steering device includes process of obtaining a speed ratio between
a steering shaft and a motor based on a mechanical angle at the
steering shaft obtained from a first steering angle and a second
steering angle and a motor electric angle of the motor, and setting
the speed ratio as a control parameter used for obtaining the
absolute rotational position of the steering wheel from the first
steering angle, the second steering angle, and the motor electric
angle at the control means.
Inventors: |
Asada, Atsuhisa; (Obu-shi,
JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
TOYODA KOKI KABUSHIKI
KAISHA
1-1, Asahi-machi, Aichi-ken
Kariya-shi
JP
|
Family ID: |
32821522 |
Appl. No.: |
10/806401 |
Filed: |
March 23, 2004 |
Current U.S.
Class: |
180/443 |
Current CPC
Class: |
G01D 2205/28 20210501;
B62D 5/0457 20130101; B62D 5/0481 20130101; B62D 15/0235 20130101;
G01D 2205/26 20210501; B62D 15/0215 20130101 |
Class at
Publication: |
180/443 |
International
Class: |
B62D 011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 27, 2003 |
JP |
2003-086785 |
Claims
1. A method for setting a control parameter for an electric power
steering device comprising: a first resolver for detecting a first
steering angle including a rotation angle of a steering shaft
connected to a steering wheel; a second resolver for detecting a
second steering angle including a rotation angle of the steering
shaft, the second resolver including pole pairs different number
from the first resolver; a rack and pinion type steering mechanism
including a rack shaft geared with a pinion shaft coaxially
connected to the steering shaft; a motor for assisting an actuation
of the rack shaft; a third resolver for detecting a motor electric
angle including a rotation angle of the motor; and a control means
for controlling the motor based on the absolute rotational position
of the steering wheel obtained from the first steering angle, the
second steering angle, and the motor electric angle; the setting
method comprising process of: obtaining a speed ratio between the
steering shaft and the motor based on a mechanical angle at the
steering shaft obtained from the first steering angle and the
second steering angle and the motor electric angle of the motor;
and setting the speed ratio as a control parameter used for
obtaining the absolute rotational position of the steering wheel
from the first steering angle, the second steering angle, and the
motor electric angle at the control means.
2. The method for setting the control parameter according to claim
1, wherein the control means includes a memory means and the speed
ratio or the control parameter is memorized at the memory
means.
3. A setting device for a control parameter of the power steering
device comprising: a first resolver for detecting a first steering
angle including a rotation angle of a steering shaft connected to a
steering wheel; a second resolver for detecting a second steering
angle including a rotation angle of the steering shaft, the second
resolver including pole pairs different number from the first
resolver; a rack and pinion type steering mechanism including a
rack shaft geared with a pinion shaft coaxially connected to the
steering shaft; a motor for assisting an actuation of the rack
shaft; a third resolver for detecting a motor electric angle
including a rotation angle of the motor; and a control means for
controlling the motor based on the absolute rotational position of
the steering wheel obtained from the first steering angle, the
second steering angle, and the motor electric angle, the setting
device comprising: a speed ratio calculation means for obtaining a
speed ratio between the pinion shaft and the motor based on a
mechanical angle at the pinion shaft side obtained from the first
steering angle and the second steering angle and the motor electric
angle of the motor; and a parameter setting means for setting the
obtained speed ratio at the control means as a control parameter
used for obtaining the absolute rotational position of the steering
wheel from the first steering angle, the second steering angle, and
the motor electric angle.
4. The setting device for the control parameter according to claim
3, wherein the control means includes a memory means and the speed
ratio or the control parameter are memorized in the memory
means.
5. An electric power steering device comprising: a first resolver
for detecting a first steering angle including a rotation angle of
a steering shaft connected to a steering wheel; a second resolver
for detecting a second steering angle including a rotation angle of
the steering shaft, the second resolver including pole pairs
different number from the first resolver; a rack and pinion type
steering mechanism including a rack shaft geared with a pinion
shaft coaxially connected to the steering shaft; a motor for
assisting an actuation of the rack shaft; a third resolver for
detecting a motor electric angle including a rotation angle of the
motor; and a control means for controlling the motor based on the
absolute rotational position of the steering wheel obtained from
the first steering angle, the second steering angle, and the motor
electric angle; wherein the motor is controlled based on the
absolute rotational position of the steering wheel obtained from
the first steering angle, the second steering angle, and the motor
electric angle using a control parameter set by a setting method of
the control parameter, the setting method comprising process of:
obtaining a speed ratio between the steering shaft and the motor
based on a mechanical angle at the steering shaft obtained from the
first steering angle and the second steering angle and the motor
electric angle of the motor; and setting the speed ratio as a
control parameter used for obtaining the absolute rotational
position of the steering wheel from the first steering angle, the
second steering angle, and the motor electric angle at the control
means.
6. The electric power steering device according to claim 5, wherein
the control means includes a memory means and the speed ratio or
the control parameter is memorized at the memory means.
7. An electric power steering device comprising: a first resolver
for detecting a first steering angle including a rotation angle of
a steering shaft connected to a steering wheel; a second resolver
for detecting a second steering angle including a rotation angle of
the steering shaft, the second resolver including pole pairs
different number from the first resolver; a rack and pinion type
steering mechanism including a rack shaft geared with a pinion
shaft coaxially connected to the steering shaft; a motor for
assisting an actuation of the rack shaft; a third resolver for
detecting a motor electric angle including a rotation angle of the
motor; and a control means for controlling the motor based on the
absolute rotational position of the steering wheel obtained from
the first steering angle, the second steering angle, and the motor
electric angle; wherein the motor is controlled based on the
absolute rotational position of the steering wheel obtained from
the first steering angle, the second steering angle, and the motor
electric angle using the control parameter set by a setting device
of a control parameter, further comprising: a speed ratio
calculation means for obtaining a speed ratio between the steering
shaft and the motor based on a mechanical angle at the steering
shaft obtained from the first steering angle and the second
steering angle and the motor electric angle of the motor; and a
parameter setting means for setting the obtained speed ratio at the
control means as a control parameter used for obtaining the
absolute rotational position of the steering wheel from the first
steering angle, the second steering angle, and the motor electric
angle.
8. The electric power steering device according to claim 7, wherein
the control means includes a memory means and the speed ratio or
the control parameter are memorized in the memory means.
Description
INCORPORATION BY REFERENCE
[0001] This application is based on and claims priority under 35
U.S.C. .sctn. 119 with respect to Japanese Patent Application No.
2003-086785 filed on Mar. 27, 2003, the entire contents of which
are incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to a setting method for a
control parameter, a setting device for a control parameter, and an
electric power steering device.
BACKGROUND OF THE INVENTION
[0003] A known electric power steering device reduces the steering
force by a steering wheel by providing the assisting force to a
steering mechanism connected to a steering shaft by a motor. With
the known electric power steering device, the steering wheel
rotates within a predetermined limited rotation number or greater
than a single rotation in the clockwise direction and in the
counterclockwise direction respectively. A position of the steering
wheel at which the vehicle moves straight is determined as a
neutral position. Thus, a steering angle is obtained by detecting
the absolute position of the steering wheel, i.e., by detecting the
rotation angle of the steering wheel relative to the neutral
position.
[0004] A known absolute position detection device described in
Japanese Patent Laid-Open Publication No. 2003-75109 is disclosed
as the sensor for detecting the steering angle by the steering
wheel. With the known absolute position detection device described
in Japanese Patent Laid-Open Publication No. 2003-75109, the number
of pole pairs of a second resolver serving as a part of a torque
sensor for detecting the steering torque of the steering wheel and
the number of pole pairs of a motor resolver for detecting a motor
rotation angle of an assisting motor are determined different from
each other. With this construction, the absolute rotational
position of the steering wheel is detected by using the
characteristics that a difference of detection signal waveforms
generated by a cycle difference of detection signals detected from
the second resolver and the motor resolver assumes a predetermined
amount based on a speed ratio between the steering wheel and the
assisting motor.
[0005] Notwithstanding, with the known absolute position detection
device described in Japanese Patent Laid-Open Publication No.
2003-75109, the speed ratio between the steering wheel and the
assisting motor is determined based on a predetermined proportional
stroke S and a predetermined lead L serving as a design value, or
the like. In this case, the proportional stroke S corresponds to a
moving amount of a rack shaft of a rack and pinion mechanism when
the steering wheel is rotated by a single rotation. The lead L
corresponds to the moving amount of the rack shaft when the
assisting motor is rotated by a single rotation. The speed ratio is
calculated by S/L.
[0006] Accordingly, in case, for example, a pinion gear and a rack
groove, or the like, included in the rack and pinion gear mechanism
have the machining error and the dispersion, or the like, the error
is generated at the speed ratio determined by the predetermined
design value, or the like. Further, the error is generated at the
quantitative difference of the detection signal waveforms. Thus, it
becomes difficult to accurately detect the absolute rotational
position of the steering wheel.
[0007] A need thus exists for the present invention to provide a
setting method of a control parameter and a setting device of the
control parameter which enables to determine the control parameter
for accurately detecting the absolute rotational position of the
steering wheel at an electric power steering device. A need further
exists for the present invention to provide an electric power
steering device which accurately detects the absolute rotational
position of the steering wheel and controls a motor for assisting
the steering based on the absolute rotational position.
SUMMARY OF THE INVENTION
[0008] In light of the foregoing, the present invention provides a
method for setting a control parameter for an electric power
steering device which includes a first resolver for detecting a
first steering angle including a rotation angle of a steering shaft
connected to a steering wheel, a second resolver for detecting a
second steering angle including a rotation angle of the steering
shaft, the second resolver including pole pairs different number
from the first resolver, a rack and pinion type steering mechanism
including a rack shaft geared with a pinion shaft coaxially
connected to the steering shaft, a motor for assisting an actuation
of the rack shaft, a third resolver for detecting a motor electric
angle including a rotation angle of the motor, and a control means
for controlling the motor based on the absolute rotational position
of the steering wheel obtained from the first steering angle, the
second steering angle, and the motor electric angle. The setting
method includes process of obtaining a speed ratio between the
steering shaft and the motor based on a mechanical angle at the
steering shaft obtained from the first steering angle and the
second steering angle and the motor electric angle of the motor,
and setting the speed ratio as a control parameter used for
obtaining the absolute rotational position of the steering wheel
from the first steering angle, the second steering angle, and the
motor electric angle at the control means.
[0009] According to another aspect of the present invention, a
setting device for a control parameter of the power steering device
includes a first resolver for detecting a first steering angle
including a rotation angle of a steering shaft connected to a
steering wheel, a second resolver for detecting a second steering
angle including a rotation angle of the steering shaft, the second
resolver including pole pairs different number from the first
resolver, a rack and pinion type steering mechanism including a
rack shaft geared with a pinion shaft coaxially connected to the
steering shaft, a motor for assisting an actuation of the rack
shaft, a third resolver for detecting a motor electric angle
including a rotation angle of the motor, a control means for
controlling the motor based on the absolute rotational position of
the steering wheel obtained from the first steering angle, the
second steering angle, and the motor electric angle. The setting
device includes a speed ratio calculation means for obtaining a
speed ratio between the steering shaft and the motor based on a
mechanical angle at the steering shaft obtained from the first
steering angle and the second steering angle and the motor electric
angle of the motor, and a parameter setting means for setting the
obtained speed ratio at the control means as a control parameter
used for obtaining the absolute rotational position of the steering
wheel from the first steering angle, the second steering angle, and
the motor electric angle.
[0010] According to still further aspect of the present invention,
an electric power steering device includes a first resolver for
detecting a first steering angle including a rotation angle of a
steering shaft connected to a steering wheel, a second resolver for
detecting a second steering angle including a rotation angle of the
steering shaft, the second resolver including pole pairs different
number from the first resolver, a rack and pinion type steering
mechanism including a rack shaft geared with a pinion shaft
coaxially connected to the steering shaft, a motor for assisting an
actuation of the rack shaft, a third resolver for detecting a motor
electric angle including a rotation angle of the motor, and a
control means for controlling the motor based on the absolute
rotational position of the steering wheel obtained from the first
steering angle, the second steering angle, and the motor electric
angle. The motor is controlled based on the absolute rotational
position of the steering wheel obtained from the first steering
angle, the second steering angle, and the motor electric angle
using a control parameter set by a setting method of the control
parameter. The setting method includes process of obtaining a speed
ratio between the steering shaft and the motor based on a
mechanical angle at the steering shaft obtained from the first
steering angle and the second steering angle and the motor electric
angle of the motor, and setting the speed ratio as a control
parameter used for obtaining the absolute rotational position of
the steering wheel from the first steering angle, the second
steering angle, and the motor electric angle at the control
means.
[0011] According to still another aspect of the present invention,
an electric power steering device includes a first resolver for
detecting a first steering angle including a rotation angle of a
steering shaft connected to a steering wheel, a second resolver for
detecting a second steering angle including a rotation angle of the
steering shaft, the second resolver including pole pairs different
number from the first resolver, a rack and pinion type steering
mechanism including a rack shaft geared with a pinion shaft
coaxially connected to the steering shaft, a motor for assisting an
actuation of the rack shaft, a third resolver for detecting a motor
electric angle including a rotation angle of the motor, and a
control means for controlling the motor based on the absolute
rotational position of the steering wheel obtained from the first
steering angle, the second steering angle, and the motor electric
angle. The motor is controlled based on the absolute rotational
position of the steering wheel obtained from the first steering
angle, the second steering angle, and the motor electric angle
using the control parameter set by a setting device of a control
parameter. The electric power steering device further includes a
speed ratio calculation means for obtaining a speed ratio between
the steering shaft and the motor based on a mechanical angle at the
steering shaft obtained from the first steering angle and the
second steering angle and the motor electric angle of the motor,
and a parameter setting means for setting the obtained speed ratio
at the control means as a control parameter used for obtaining the
absolute rotational position of the steering wheel from the first
steering angle, the second steering angle, and the motor electric
angle.
BRIEF DESCRIPTION OF THE DRAWING FIGURES
[0012] The foregoing and additional features and characteristics of
the present invention will become more apparent from the following
detailed description considered with reference to the accompanying
drawing figures in which like reference numerals designate like
elements.
[0013] FIG. 1 is an overview showing an electric power steering
device according to an embodiment of the present invention.
[0014] FIG. 2 is an enlarged view of a part of the electric power
steering device in an ellipse indicated with a chain dotted II as
shown in FIG. 1.
[0015] FIG. 3 is an enlarged view of a part of the electric power
steering device in an ellipse indicated with a chain dotted III as
shown in FIG. 1.
[0016] FIG. 4 is a block view showing a connecting construction
between an ECU for controlling the electric power steering device
and a resolver according to the embodiment of the present
invention.
[0017] FIG. 5 is a characteristic view showing resolver output
signals of a first resolver and a second resolver relative to a
rotation angle of a steering wheel and a mechanical angle of the
steering wheel.
[0018] FIG. 6 is a flowchart showing a flow of a control parameter
setting transaction carried out by an ECU shown in FIG. 4.
DETAILED DESCRIPTION OF THE INVENTION
[0019] One embodiment of the present invention will be explained
with reference to the illustrations of the drawing figures as
follows.
[0020] An embodiment of a setting method of a control parameter of
the present invention and an embodiment of an electric power
steering device of the present invention will be explained
referring to FIGS. 1-6.
[0021] As shown in FIGS. 1, 4, an electric power steering device 20
includes a steering wheel 21, a steering shaft 22, a pinion shaft
23, a rack shaft 24, a torque sensor 30, a motor 40, a motor
resolver 44, a ball screw mechanism 50, and an ECU 60 serving as a
control means. The steering state of steering wheel 21 is detected
by the torque sensor 30, and the motor 40 generates the assisting
force in accordance with the steering state to assist the steering
operation of an operator. Vehicle wheels are connected to the both
sides of the rack shaft 24 via tie rods respectively.
[0022] As shown in FIGS. 1-2, a first end of the steering shaft 22
is connected to the steering wheel 21. A second end of the steering
shaft 22 is connected to an input shaft 23a of the pinion shaft 23
and the input shaft 23a is connected to a first end of a torsion
bar 31 by a pin 32. A second end 31a of the torsion bar 31 is
connected to an output shaft 23b of the pinion shaft 23 with spline
connection.
[0023] The input shaft 23a of the pinion shaft 23 is rotatably
supported in a pinion housing 25 by a bearing 33a. The output shaft
23b is supported in the pinion housing 25 by a bearing 33b. A first
resolver 35 is provided between the input shaft 23a and the pinion
housing 25. A second resolver 37 is provided between the output
shaft 23b and the pinion housing 25. The first resolver 35 and the
second resolver 37 included in the torque sensor 30 detects the
steering angle of the steering wheel 21 and are electrically
connected to the ECU 60 via a terminal 39 as shown in FIG. 4.
[0024] A pinion gear 23c is formed at an end portion of the output
shaft 23b of the pinion shaft 23. The pinion gear 23c is
selectively geared with a rack groove 24a of the rack shaft 24. As
foregoing, the rack and pinion steering mechanism is
constructed.
[0025] As shown in FIGS. 1-3, the rack shaft 24 is accommodated in
the rack housing 26 and the motor housing 27. A ball screw grooves
24b are spirally formed at intermediate portions of the rack shaft
24. A cylindrical motor shaft 43 supported by a bearing 29 is
provided about the ball screw groove 24b to be rotatable coaxially
with the rack shaft 24. The motor shaft 43 is included in the motor
40 likewise a stator 41 and an excitation coil 42, or the like. The
magnetic field generated by the excitation coil 42 wound around the
stator 41 affects a permanent magnet 45 provided at an external
periphery of the motor shaft 43 serving as a rotor to rotate the
motor shaft 43.
[0026] A ball screw nut 52 is provided at an internal periphery of
the motor shaft 43. A ball screw groove 52a is formed at the ball
screw nut 52 spirally. Thus, a ball screw mechanism 50 for moving
the rack shaft 24 in the axial direction by the rotation of the
motor shaft 43 is constructed by providing numbers of balls 54
between the ball screw groove 52a of the ball screw nut 52 and the
ball screw groove 24b of the rack shaft 24.
[0027] In other words, the rotational torque in the normal and
reverse directions of the motor shaft 43 is converted into the
reciprocating motion in the axial direction of the rack shaft 24.
Accordingly, the reciprocating motion serves as the assisting force
for reducing the steering force of the steering wheel 21 via the
pinion shaft 23 included in the rack and pinion type steering
mechanism.
[0028] A motor resolver 44 for detecting a rotation angle (i.e., an
electric angle) .theta.Me of the motor shaft 43 is provided between
the motor shaft 43 of the motor 40 and the motor housing 27. The
motor resolver 44 serving as a third resolver is electrically
connected to the ECU 60 via terminals.
[0029] The ECU 60 serving as the control means, a speed ratio
calculation means, and a parameter setting means includes a CPU 61,
a nonvolatile memory 62 serving as a memory means, and amplifiers
63, 64, 65. The CPU 61 is electrically connected to the first
resolver 35, the second resolver 37, and the motor resolver 44 via
the amplifiers 63, 64, 65. The CPU 61 is further connected to the
nonvolatile memory 62 and a semiconductor memory device serving as
a main memory device, or the like via a system bus. A program, or
the like, regarding a control. parameter setting transaction is
stored in a main memory device. The nonvolatile memory 62 includes
EEPROM such as a flash memory, a magnetic memory device such as a
hard disc device, and an optical magnetic memory device such as a
MO disc device, or the like.
[0030] Regarding the construction of the first resolver 35, the
second resolver 37, and the motor resolver 44 and the electric
characteristics thereof, Japanese Patent Laid-Open Publication No.
2003-75109 (corresponding to U.S. patent application Ser. No.
10/233,495), Japanese Patent Application No. 2002-196131
(corresponding to International Patent Publication No. WO
2004/005843A1), and Japanese Patent Application No. 2003-73807 are
incorporated herein by reference.
[0031] With the construction of the first resolver 35, the second
resolver 37, and the motor resolver 44 described in Japanese Patent
Laid-Open Publication No. 2003-75109, Japanese Patent Application
No. 2002-196131, and Japanese Patent Application No. 2003-73807,
the rotation angle of the steering shaft 22, i.e., the mechanical
angle .theta.Tm of the steering wheel 21 (i.e., the mechanical
angle of the pinion shaft side) can be detected by a first steering
angle .theta.T1 by the first resolver 35 and a second steering
angle .theta.T2 by the second resolver 37. Moreover, the torsion of
the torsion bar 31 in accordance with the steering torque can be
detected as a torsion angle from an angle difference between the
first steering angle .theta.T1 and the second steering angle
.theta.T2 and the angle ratio, or the like.
[0032] Because a steering torque T is calculated from a relative
rotation angle difference .DELTA..theta. serving as the torsion
angle of the torsion bar 31 and the rigidity of the torsion bar 31,
the steering operation of the operator can be assisted by the
steering force generated by the motor 40 by conducting the
assisting control for assisting the steering force in accordance
with the steering torque T by the CPU 61 of the ECU 60.
[0033] The first resolver 35 included in the torque sensor 30 has
five pole pairs (10 poles) corresponding to including five pairs of
the N poles and the S poles electrically. Thus, the first steering
angle (i.e., electric angle) .theta.T1 obtained from the first
resolver 35 forms five peaks by a rotation (i.e., mechanically 360
degrees) of the steering wheel 21. Because the first resolver 35
outputs the electric angle corresponding to five times of one
rotation relative to the mechanical angle 360 degrees (i.e.,
360.degree..multidot.5=1800.degree.), the first resolver 35
includes the resolution five times of the resolver which has one
pole pair.
[0034] In the meantime, the second steering angle (i.e., electric
angle) .theta.T2 obtained from the second resolver 37 included in
the torque sensor 30 forms six peaks by the rotation (i.e.,
mechanically 360.degree.) of the steering wheel 21. Because the
second resolver 37 has six pole pairs (twelve poles) corresponding
to including six pairs of the N poles and the S poles electrically,
the electric angle corresponding to six times of the rotation
relative to the mechanical angle 360.degree. (i.e.,
360.degree..multidot.6=2160.degree.) is outputted. Thus, the second
resolver 37 includes the resolution six times of the resolver which
has one pole pair.
[0035] Thus, the first resolver 35 outputs the electric angle
.theta.T1 as the resolver output signal and the second resolver 37
outputs the electric angle .theta.T2 as the resolver output signal.
As shown in FIG. 5, the waveforms of the output signals of the
electric angle .theta.T1 and the electric angle .theta.T2 do not
show the same waveforms at the rotation angle of the steering wheel
21. Thus, by conducting the calculation transaction by the CPU 61
based on the electric angle .theta.T1 of the first resolver 35 and
the electric angle .theta.T2 of the second resolver 37, the
mechanical angle .theta.Tm of the high resolution can be attained
relative to the rotation of the steering wheel 21.
[0036] As shown in FIG. 5, with the electric power steering device
20 because the steering wheel 21 rotates two rotations in the
clockwise direction and in the counterclockwise direction from the
neutral point, each rotational amount (A=1, 0, -1, -2) cannot be
identified by the first and the second resolvers 35, 37 included in
the torque sensor 30. Thus, the motor rotational angle (i.e.,
electric angle .theta.Me) of the motor 40 is detected by the motor
resolver 44 and a calculated motor electric angle .theta.Me (A) is
calculated by the ECU 60.
[0037] In other words, four calculated motor electric angles
.theta.Me(1), .theta.Me(0), .theta.Me (-1), .theta.Me(-2)
corresponding to A=1, 0, -1, -2 are calculated at the calculation
transaction by a formula 1. Further, after rounding off four
calculated motor electric angles .theta.Me (A) within a
predetermined range, the value closest to an actual motor electric
angle .theta.Me (distinguished from the calculated motor electric
angles .theta.Me (A)) is selected from each rotational amount (A=1,
0, -1, -2).
.theta.Me (A)=(.theta.Tm+360.multidot.A).multidot.r [Formula 1]
[0038] As shown in FIG. 5, even when the steering wheel sensor 21
rotates within the limited rotation number equal to or greater than
one rotation in the clockwise direction and the counterclockwise
direction, the absolute rotational position of the steering wheel
21 can be detected by the first resolver 35, the second resolver
37, and the motor resolver 44 included in the torque sensor 30.
[0039] Wherein, r corresponds to the product value of a
deceleration gear ratio of the ball screw mechanism 50 and the
number of pole pairs of the motor resolver 44, which assumes a
non-integer including the decimal place. For example, in case the
deceleration gear ratio of the ball screw mechanism 50 is
determined at 8.2 and the number of pole pairs of the motor
resolver 44 is determined at 7, the product value r equals to 57.4
(r=8.2.multidot.7). In the present embodiment, the number of pole
pairs of the motor resolver 44 is set to be same as the number of
the pole pairs of the motor 40.
[0040] In other word, the deceleration gear ration of the ball
screw mechanism 50 is a speed ratio Mrev between the rotational
amount of the steering wheel 21 (i.e. steering shaft 22) and the
rotational amount of the motor 40. Therefore, the product value r
is obtained as a product of the speed ratio Mrev and number of pole
pair of the motor resolver 44. The speed ratio Mrev may be defined
as the rotation number of the motor 40 when the steering wheel 21
rotates by one rotation. The speed ratio Mrev is obtained by
dividing the proportional stroke S by the lead L. In other words,
the speed ratio Mrev is obtained by dividing the proportional
stroke S corresponding to the moving amount of the rack shaft 24
when the steering wheel 21 is rotated by one rotation by the lead L
corresponding to the moving amount of the rack shaft 24 when the
motor 40 is rotated by one rotation (Mrev=S/L). A predetermined
value such as a design value may be set as the speed ratio.
[0041] In case the predetermined value such as the design value is
set as the speed ratio Mrev, the error is provided at the speed
ratio Mrev when the machining error and the dispersion, or the
like, is generated at the mechanical parts such as the pinion gear
23c of the pinion shaft 23 and the rack groove 24a of the rack
shaft 24 included in the steering mechanism. Thus, the error
included in the speed ratio Mrev directly influences on the product
value r obtained as the product between the speed ratio Mrev and
the number of pole pairs P. Thus, the precision of the calculated
motor electric angle .theta.Me (A) calculated from the formula 1 is
declined, which may cause the wrong selection when selecting the
value closest to the actual motor electric angle .theta.Me from
rotational mounts (A=1, 0, -1, -2).
[0042] With the electric power steering device 20, the speed ratio
Mrev unlikely including the error is calculated by the parameter
determination transaction shown in FIG. 6 so that the speed ratio
Mrev is defined as the control parameter. The control parameter
setting transaction shown in FIG. 6 is conducted by carrying out
the program stored in the main memory device included in the ECU 60
by the CPU 61.
[0043] As shown in FIG. 6, each electric angle .theta.T1,
.theta.T2, .theta.Me of respective resolvers varied within the
range equal to or greater than the predetermined angle is
integrated at Steps S101-S107 at the control parameter setting
transaction.
[0044] At Step S101, the first steering angle (i.e., electric
angle) .theta.T1 detected by the first resolver 35, the second
steering angle (i.e. electric angle) .theta.T2 detected by the
second resolver 37, and the actual motor electric angle .theta.Me
of the motor shaft 43 detected by the motor resolver 44 are
obtained. Thereafter, at Step S103, the mechanical angle (i.e., the
mechanical angle at the pinion shaft 23 side) .theta.Tm of the
steering wheel 21 is calculated from the electric angles .theta.T1,
.theta.T2. The transaction for integrating the calculated
mechanical angle .theta.Tm and the actual motor electric angle
.theta.Me by the last calculated values thereof respectively is
conducted at Step S105.
[0045] Whether the integration transaction is conducted within the
range equal to or greater than the predetermined angle is judged at
Step S107. In case it is not judged that the integration is
conducted within the range of equal to or greater than the
predetermined angle (i.e., No at Step 107), the transaction is
returned to Step S101 to conduct the transactions to Step S105 to
further integrate the mechanical angle .theta.Tm and the actual
motor electric angle .theta.Me respectively. The predetermined
angle of the range equal to or greater than the predetermined angle
judged at Step S107 may be, for example,. defined as 1440 degrees
corresponding to the four rotations of the steering wheel 21, as
360 degrees corresponding to one rotation of the steering wheel 21,
and 90 degrees corresponding to one fourth rotations of the
steering wheel 21, or the like. In the meantime, in case it is
judged that the integration is conducted within the range equal to
or greater than the predetermined angle at Step S107 (i.e., Yes at
S107), the speed ratio Mrev between the steering wheel 21 and the
motor 40 is calculated at the consecutive transaction at Step
S109.
[0046] At Step S109, the speed ratio Mrev between the steering
wheel 21 and the motor 40 is calculated by a formula 2 based on the
mechanical angle .theta.Tm of the steering wheel 21 and the actual
motor electric angle .theta.Me integrated respectively at Steps
S101-107.
Mrev=.intg..theta.Me/(.intg..theta.Tm.multidot.P) [Formula 2]
[0047] Wherein, P indicates the number of pole pairs of the motor
resolver 44.
[0048] For example, in case the mechanical angle .theta.Tm of 1440
degrees corresponding to the four rotations of the steering wheel
21 and the actual motor electric angle .theta.Me are integrated at
Steps S101-S107, for example supposing that the mechanical error
and the dispersion are not exist, .intg..theta.Me assumes
82656(=1440.multidot.57. 4) and .intg..theta.Tm.multidot.P assumes
10080(=1440.multidot.7). Thus, the speed ratio Mrev is calculated
as 8.2(=82656/10080). Step 109 serves as a speed ratio calculation
means.
[0049] At Step S111, the speed ratio calculated at Step S109 is set
as the control parameter of the electric power steering device 20.
Step S111 serves as a parameter setting means. For example, the
speed ratio Mrev may be set as the control parameter used for
obtaining the product value r(=Mrev.multidot.P) of formula 1. In
the foregoing example, because the value of the speed ratio Mrev is
obtained as 8.2, by determining the speed ratio Mrev as the control
parameter, the product value r is determined as
57.4(=8.2.multidot.7).
[0050] The speed ratio Mrev may be set each time by the control
parameter setting transaction. However, because setting the speed
ratio Mrev each time increases the calculation transaction load at
the CPU 61 of the ECU 60, the transaction load of the CPU 61 is
reduced by reading the once obtained speed ratio Mrev and memorized
in the memory device. By setting the speed ratio Mrev regularly
(e.g., by ten minutes or by one hour) by the control parameter
setting transaction, the speed ratio Mrev considering to the
dispersion, or the like, is set as the control parameter when the
dispersion, or the like, is generated at the mechanical parts, or
the like, of the steering mechanism due to the temperature change
and the change per time. In this case, the control parameter
setting transaction is regularly started by a timer transaction, or
the like, for calculating a predetermined period.
[0051] At Step S113, the speed ratio Mrev calculated at Step S109
is written in the nonvolatile memory. More particularly, for
example, the information (data) concerning to the speed ratio Mrev
is written in the nonvolatile memory 62 (e.g., EEPROM such as the
flash memory) included in the ECU 60 to be memorized therein. Thus,
for example, at the inspection process at the shipment of the
electric power steering device 20 and at a maintenance process
after the shipment, or the like, the calculated speed ratio Mrev is
memorized in the ECU 60 by carrying out the control parameter
setting transaction.
[0052] As foregoing, with the electric power steering device 20,
the speed ratio Mrev between the mechanical angle .theta.Tm of the
steering wheel 21 and the motor 40 is obtained based on the
mechanical angle .theta.Tm of the steering wheel 21 obtained from
the first steering angle .theta.T1 detected by the first resolver
35 and the second steering angle .theta.T2 detected by the second
resolver 37, and the actual motor electric angle .theta.Me detected
by the motor resolver 44 (S109). Thereafter, the speed ratio Mrev
is set as the control parameter used for providing the product
value r(=Mrev.multidot.P) of the formula 1 for obtaining the
calculated motor electric angle .theta.Me (A) (A=-2, -1, 0, 1)
(S111).
[0053] Thus, for example, the speed ratio Mrev may be obtained
considering the machining error and the dispersion generated at the
rack groove 24a of the rack groove 24 and the pinion gear 23c of
the pinion shaft 23, or the like, included in the steering
mechanism. Accordingly, the speed ratio Mrev obtained considering
the error, or the like, generated at the mechanical parts such as
the steering mechanism can be set as the control parameter of the
electric power steering device 20. Thus, the control parameter for
accurately detecting the absolute rotational position of the
steering wheel 21 relative to the electric power steering device 20
is attained. With the electric power steering device 20 set with
the speed ratio Mrev, the absolute rotational position of the
steering wheel 21 can be accurately detected to control the motor
40 for assisting the steering operation based on the absolute
rotational position.
[0054] Although the embodiment of the present invention is
explained with the electric power steering device 20, the
embodiment of the present invention is not limited. For example,
the ECU 60 included in the electric power steering device 20 may be
constructed as an independent computer system (i.e., including a
CPU, a memory device, an input-output device, an interface device,
or the like) separated from the electric power steering device 20
and a control parameter setting system for executing the control
parameter setting transaction shown in FIG. 6 by the computer
system may be constructed. In this case, the obtained speed ratio
Mrev is memorized in a memory device (including the nonvolatile
memory) included in the ECU 60 of the electric power steering
device 20. Accordingly, the speed ratio Mrev can be set at the
electric power steering device 20 without applying the load at the
ECU 60 of the electric power steering device 20.
[0055] According to the embodiment of the present invention, the
mechanical angle of the steering shaft is determined by the first
resolver and the second resolver, and the motor electric angle of
the motor is detected by the third resolver. Thus, for example, the
speed ratio can be obtained considering the dispersion and the
machining error, or the like, generated at the rack and the pinion
gear included in the steering mechanism. Accordingly, the speed
ratio obtained considering the error, or the like, generated at the
mechanical parts of the steering mechanism, or the like, can be set
as the control parameter of the electric power steering device,
which allows to set the control parameter for accurately detecting
the absolute rotational position of the steering wheel relative to
the electric power steering device. With the electric power
steering device set with the foregoing speed ratio, the absolute
rotational position of the steering wheel can be accurately
detected.
[0056] According to the embodiment of the present invention, the
control means includes the memory means for memorizing the speed
ratio or the control parameter. Thus, after obtaining the speed
ratio, it may not be required to obtain the speed ratio by reading
in the speed ratio from the memory means. Accordingly, it is not
necessary to obtain the speed ratio every time by the control means
of the electric power steering device, which reduces the
transaction load of the control means to enable the high speeding
of the transaction speed.
[0057] According to the embodiment of the present invention, the
motor is controlled based on the absolute rotational position of
the steering wheel obtained from the first steering angle, the
second steering angle, and the motor electric angle using the
control parameter set by the control parameter setting device or
the setting method of the control parameter. Because the speed
ratio obtained considering the error, or the like, likely to be
generated at the mechanical pasts of the steering mechanism, or the
like, included in the electric power steering device is set as the
control parameter of the electric power steering device, the
absolute rotational position of the steering wheel can be
accurately detected using the control parameter. Thus, the absolute
operational position of the steering wheel can be accurately
detected to control the motor for assisting the steering operation
based on the absolute operational position.
[0058] The principles, preferred embodiment and mode of operation
of the present invention have been described in the foregoing
specification. However, the invention which is intended to be
protected is not to be construed as limited to the particular
embodiment disclosed. Further, the embodiment described herein is
to be regarded as illustrative rather than restrictive. Variations
and changes may be made by others, and equivalents employed,
without departing from the spirit of the present invention.
Accordingly, it is expressly intended that all such variations,
changes and equivalents which fall within the spirit and scope of
the present invention as defined in the claims, be embraced
thereby.
* * * * *